Apparatus for measuring corrosion rates



Dec. 3, 1963 .'w. GERHARDT 3,112,641

APPARATUS FOR MEASURING CORROSION RATES Original Filed June 9, 1955DEFZECT/M -//VC//6' ATTOKMEKS United States Patent 3,112,641 APPARATUSF012 MEASURING CQRRGSEON RATES Carl W. G hardt, 2945' Dryden Road,Dayton, Ghio Griginai application dune 9, 1955, fier. No. 514,408, new

Patent No. 2,972,248, dated Feb. 21, 1961. Divided this appiicationSept. 7, 196%, Ser. No. 54,553

1 'jlaim. (Ci. 73-86) (Granted under This 35, US. Code (1952), see. 266)The invention described herein may be manufactured and used by or forthe United States Government for governmental purposes Without paymentto me of any royaity thereon.

This invention is a division of my copending appiication Serial Number514,408, filed June 9, 1955 which matured into United States Fatent No.2,972,248 and relates to an apparatus for measuring the corrosivity ofan atmosphere or environment or for measuring the corrodibility of aresilient member such as a spring. This invention could also be used tomeasure erosive rates.

The conventional method to measure corrosivity or" an environment or thecorrodibiiity of material is to prepare a test sample or samples, putthem in a corrosive environment and measure the loss in weight or" thesamples after a fixed period of time. Such a method requires anextremely accurate balance and it has been necessary to run a largenumber of samples averaging results to make any reasonably accurateestimation of corrosiveness. There seem to be a number of factors thatinfluence the accuracy of this method including the original preparationof the samples and the handling and preparation of the samples afterexposure prior to weight is an object of this invention to provide animproved apparatus for testing corrosion rates wherein a measurement ismade indicative of the change of strength of a resilient member withtime as an indication of corrosion rate.

it is another object of this invention to provide an improved apparatusfor measuring the corrosivity of an environment or an atmosphere whereinsuch information is obtained from a measurement indicative of the changeof strength with time of the resilient member.

it is a further object of this invention to provide an improvedapparatus for measuring the corrosion rate or" a resilient material suchas a sprin wherein such information is obtained from a measurementindicative of the change of strength of the resilient member.

It is yet another object of this invention to provide an improvedapparatus for testing erosion rates wl erein a measurement is madeindicative of the change of strength of a resilient member with time asan indication of the erosion rate.

These and other objects of the invention will become apparent as thedetailed description of the invention proceeds.

The invention will be more clearly understood from the followingdetailed description of specific examples thereof read in conjunctionwith the accompanying drawing wherein:

FIGURE 1 is an elevational view of an embodiment of my invention; and

FIGURE 2 is a typical graphical presentation of the data obtained froman embodiment of my invention such as is shown in FIGURE 1.

Referring now to the drawing, FIGURE 1 shows an embodiment of myinvention. This embodiment has a channel shaped frame 28 which rests onany convenient support 27, e.g., a table. Frame 28 has a base member 28awhich supports the support members 29a and 29b in an upright position.Support member 29:: has a circular illilbdl Patented Dec. 3, 1963 recessEda therein and support member 2912 has a circular recess 3% therein.The openings of these two recesses face each other. A helical spring 31is rigidly positioned in recess 34in by welding or other suitable meansand a helical spring 32 is rigidly positioned in recess 3% in likemanner. These springs extend toward each other and are parallel to basemember 28a. A pointer 33 having circular recesses 34a and 34b therein ispositioned between support members 29a and 2%. Spring 31 is rigidlypositioned in recess 34a and spring 32 is rigidly positioned in recess34b. This arrangement puts both springs in tension pulling against oneanother through the link medium of pointer 33. The pointer has asharpened upper end to facilitate reading on scale 35 which ispositioned in close relation to pointer 33 and is supported by anysuitable support 3d. Alternatively springs 31 and 32 may be incompression against each other in which case it will not be necessary toweld or otherwise permanently fix the springs in recesses Siia, 3%, 34aand 341;.

This scale 35 may be rigidly fixed to a permanent support 36 and theapparatus positioned with the pointer opposite the zero position of thescale at the start of a test. One of the springs, e.g., spring 31, mustbe made of a material which will corrode with a measurable loss ofstrength with time. The other spring can be made of material or coatedin such a fashion that it wiil have no appreciable loss of strength withtime. Or the springs 31 or 32 may be made of different material whichwill corrode and lose strength at iiierent rates. In any event to get areading on the scale with time there must be some movement of thepointer from the Zero position and this, of course, will be madepossible by any one of the methods described above. Data obtained in theuse of this apparatus may be plotted for best use in the manner shown inFIGURE 2 or the data may be used directly in estimating corrosivity.

The apparatus of FTGURE 1 when used is placed in the particularenvironment to which it is to be exposed. The pointer 33 is positionedsuch that it points to the zero reading on the scale 35. A number ofdays or weeks or months are allowed to pass and a reading is taken ofthe new position of the pointer 33 with respect to the fixed cale 35.These readings are normally made at spaced intervals from time to tine.Data from these readings may be plotted in a manner similar to thatshown in FIGURE 2. A curve somewhat similar to that shown in FIGURE 2may thus be obtained. This curve is indicative of the corrosiveness ofthe particular environment or atmosphere in which the apparatus has beenplaced and of the relative corrodibility of springs 31 and 32. Obviouslythe apparatus may be used to test either the environment or the springsor both. The springs are usually fabricated from a material which willshow a V measurable change in compressive strength with time in thecorrosive environment.

Although the invention has been described in terms of specifiedapparatus which is set forth in considerable detail, it should beunderstood that this is by way of illustration only and that theinvention is not necessarily limited thereto, since alternativeembodiments and operating techniques will become apaprent to thoseskilled in the art in view of the disclosure. For example, the variousembodiments of the invention can be used in the determination of erosiverates as well as corrosive rates, i.e., to determine the erosiveness ofan environment or atmosphere or the erodibility of a resilient member.The resilient member would be made of suitable erodible material formeasuring the erosiveness of an atmosphere or environment, and in manycases this material could be the same material as would be used forcorrosive rate measurements. The fact that a resilient member made ofthe same material can in many cases be used to measure both corrosiverates and erosive rates is fortunate since sometimes an environment oratmosphere will have both corrosive and erosive properties. Accordingly,modifications are contemplated which may be made Without departing fromthe spirit of the described invention or of the scope of the appendedclaim.

What is claimed is:

A corrosion rate measuring apparatus comprising a base, a first supportmember extending from said base, a second support member spaced from andopposed to said first member and extending from said base, a firstcorrodible helical spring rigidly attached to said first memberandextending toward said second member, said first spring being made ofsuch material that it will lose measurable tensile strength whenpositioned in an en vironment corrosive to said first spring, a secondhelical spring which will lose tensile strength at a slower rate bycorrosion than said first spring attached rigidly to said second memberand extending toward said first member, a pointer rigidly attached tothe free-ends of said springs, a calibrated reference means cooperatingwith said pointer to indicate the extent of linear movement of saidpointer, said springs being placed in tension opposed to each other, andmeasurements being made at spaced time intervals of the relativeposition of said pointer to give an indication of the comparativecorrosion rate of said first and second helical springs.

References Cited in the file of this patent Sheet Magnesium, by W. H.Jones, Product Engineering, September 1945, pages 580, 581.

Corrosion Testing Procedures, by F. A. Champion, Chapman & Hall(London), 1952, pages 140, 141, 14

20 applied.

